I have a Sony subwoofer for the home entertainment theater. There is a loud hum coming from the subwoofer. The hum persisits even if unplugged from the receiver. Also, I've tried a ground loop isolator and plugging it in to different outlets and using the two-prong adapters. Nothing gets rid of the hum. Any sugestions

Filter capacitors in the amplifier or a broken ground (shield) wire. Check if there is a ground lift switch in your system and try it in both on and lift positions.

Loud humming noise usually comes from a bad or missing ground connection, or a failed rectifier or filter capacitor in the power supply.

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Usually a faulty cable or blown speaker will cause a humming. If it is a constant humming I would surmise a faulty cable. On the other hand, if the humming comes and goes I would guess a faulty speaker.

see this instruction and fix it. God bless you

1. • 1
     Disconnect the coaxial cable at the back of the satellite receiver or cable box by unscrewing the coupler on the cable end.
     
     
   • 2
     Attach the cable to the RF IN jack on a surge protector and tighten the coupler clockwise.
     
     
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   • 3
     Connect a second coaxial cable from the RF OUT jack on the surge protector to the input on the cable box or satellite receiver. If this stops the hum, congratulations: You're done.
     
     
   • 4
     Unplug the subwoofer's electrical cord from the power strip or wall outlet if it is connected to the same circuit as the AV receiver. The amp in the AV receiver and the amp in the subwoofer are in conflict over the grounding of the electrical circuit.
     
     
   • 5
     Plug the subwoofer into its own surge protector and connect the surge protector to a different wall outlet than the AV receiver uses.
     
     
   • 6
     Disconnect the subwoofer cable from the back of the sub and the AV receiver if all other measures fail to stop the humming. Reverse the plug connections so the plug that had been connected to the receiver is now connected to the subwoofer. Turning the cable around may solve a problem known as ground-loop hum by reversing the shielding wire inside the cable.
     
     

Read more: http://www.ehow.com/how_6979184_eliminate-sound-home-theater-subwoofer.html#ixzz2ZdzrgBSa

Unfortunately the subwoofer should have a volume control knob, and the subwoofer for the DVD765 does not have this, that is why it is so loud, the only work around is to get an audio cable with a built in volume control knob.

. call bose customer service they can help you with some settings that will help. 877-210-3782. this is their home page http://www.bose.com/controller?url=/contact/index.jsp . you have any questions or this doesnt help let me know. -Derek

This is most likely a "ground loop" and is caused by using two different electrical outlets for the two parts of the system -- main receiver and subwoofer amp.

Try using the same electrical circuit (wall outlet) for all of the equipment in the home theater, using a power strip or strips as needed.

jd40,
Sounds like a grounding issue. The first two places to look into is the powered subwoofer and antenna. During your last test, did you leave the FM antenna and subwoofer connected? Many times the hum is directly related to the antenna and/or the subwoofer and to how they are grounded; creating a ground loop through the receivers ground on the outlet. If the antenna is grounded to the dwellings wiring, hum is inevitable and sometime you can get a ground loop hum from how or how & where the subwoofer is grounded. Try taking them completely out of the loop.

Also try taking it further back to the basics, start with the receiver plugged into a known good grounded outlet with no surge or line conditioner in the loop and nothing connected to the receiver, nothing. Use one speaker and different wire to test each speaker output while in tuner and any other mode but phono. With no signal, you will either get nothing (no hum or static) or just static in the tuner mode. No hum is a good sign. Some systems will mute the speakers if no signal is connected to eliminate the static from being produced through the speakers but a ground loop hum will most likely still be produced even in mute. If you get a hum when nothing is connected to the receiver, try looking into getting a better grounded outlet, even maybe to a different dwelling.

-Chris

the conections some where are dirty you need to unplug everything clean all connections and the hum will go away

The circuit that should be turning the sub on and off based upon the presence of an audio signal is not working correctly and the sub is trying to reproduce 60 cycle hum. The unit needs service.
Dan